Circuit interrupters



Feb. 25, 1958 A. P. sTRolvi 2,824,937 CIRCUIT INTERRUPTERS Filed Deo. 5o. 1954 2 sheets-sheet 1 Fig. 3.

Feb. 25, 1958 A. P. sTRoM CIRCUIT INTERRUPTERS 2 Sheets-Sheet 2 Filed Dec. 30. 1954 mvENToR Alban* Psi-rom. BY!I ATTOR WITNESSESI 474777,14 ZM? United AStates Patent G CIRCUIT INTERRUPTERS Albert P. Strom, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 30, 1954, Serial No. 478,636 17 claims. (Ci. 20o-14s) This invention relates to circuit interrupters in general, and, more particularly, to improved arc-extinguishing structures therefor.

A general object of my invention is to provide an improved `compressed-gas type of circuit interrupter, in which more effective operation is obtained than has been obtained in constructions hitherto used.

`A more specific object of my invention is to provide an improved compressed-gas type of circuit interrupter utilizing a grounded metallic exhaust tank as an enclosing chamber filled with gas at a relatively low pressure, and associating therewith a high-pressure gas reservoir, so that during the opening operation gas from the high pressure reservoir may be blown against the established arc and'exhausted into the lower pressure region within the exhaust tank.

. Another object is to provide an improved compressedgas circuit interrupter, which has all of the advantages of a dead-tank oil circuit interrupter, yet has the highspeed characteristics of a compressed-gas circuit interrupter.

^ .Still a further object of my invention is to provide an improved compressed-gas circuit interrupter of the type specified in the immediately preceding paragraph, which is particularly adaptable for employment with a relatively expensive gas, which it is desired to use over and over again, during repeated operations, without loss.

Another object of my invention is to provide an improved compressed-gas valve operating arrangement for a compressed-gas type of circuit interrupter.

Still a further object of my invention is to provide an improved circuit interrupter of substantially enclosed con` struction, in which a portion of the gas is maintained at high pressure, and another portion of the gas is maintained at a somewhat lower pressure, in which the advantages of a dead-tank type of construction may be taken.

Yet a further object is to provide an improved circuit interrupter of the foregoing type, in which improved means are utilized to provide a blast of gas during the closing operation as well as during the opening operation.

An additional object of my invention is to provide a circuit interrupter particularly adapted for use with sulfur hexauoride gas, the remarkable extinguishing properties of which are set out and claimed in U. S. patent application, led July 19, 1951, Serial No. 237,502, now United States Patent 2,757,261, issued July 3l, 1956, to Harry J. Lingal, Thomas E. Browne, Jr., and Albert P. Strom, entitled Circuit Interrupters and assigned to the assignee of the instant application.

Another object is to provide a circuit interrupter particularly adapted for use with selenium hexafluoride gas, the extinguishing properties of which are described and claimed in United States patent application filed September 14, 1954, S. N. 455,976, now United States Patent 2,733,316, issued January 31, 1956, to Thomas E. Browne, Jr., Albert P. Strom and Harvey E. Spindle, and assigned t9 the assignee ofthe instant application. o e

Thus, the circuit interrupters of my invention are particularly adapted to use at least one gas selected from the group consisting of sulfur hexafluoride and selenium hexauoride, or adinixed with at least one of the group consisting of helium, carbon dioxide, air, nitrogen and argon.

in a circuit interrupter utilizing a relatively expensive like SFS or SeFs, it is desirable to conserve such gas, and to use it repeatedly for subsequent operations; and my present invention has, as one of its aspects, the provision of a dead-tank type of circuit interrupter particularly suitable for utilization with such a gas.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

Figure l is a side elevational view of a circuit interrupter employing the principles of my invention, with the contacts being illustrated as being in the closed-circuit position;

rig. 2 is an enlarged view of a portion of the interior of the circuit interrupter of Fig. l, with the contacts likewise being illustrated in the closed-circuit position;

Fig. 3 is a fragmentary view, similar to that shown in lng. 2, but illustrating the contact positions during a portion of the opening operation; and

Fig. 4 is an enlarged fragmentary vertical sectional view taken substantially along the line lV-lV of Fig. 3.

f Referring to the drawings, and more particularly to Fig. l thereof, the reference numeral 1 generally designates a compressed-gas type of circuit interruptor, in this particular instance comprising a grounded metallic exhaust tank 2, of the type usually employed in dead-tank Oil circuit breakers.

As well known by those skilled in the art, such a tank construction involves a cover 3 and a pair of terminal bushings 4, 5, which insulate the conductors leading out of the enclosed apparatus from the metallic cover 3 of the exhaust tank 2.

f Referring more particularly to Fig. 2, which more clearly illustrates, in enlarged fashion, a portion of the internal construction of the exhaust tank 2 of Fig. 1, it will be observed that at the lower interior end of the terminal bushing 4 is secured an arc-extinguishing unit, generally designated by the reference numeral 7, and comprising a relatively stationary rod-shaped contact 8, and a cooperable movable rod-shaped contact 9, the latter being secured to and movable with an extremity of the conducting bridging member 10, which is actuated by the usual lift rod 11, as more fully disclosed in Fig. 1. Any suitable mechanism, either pneumatic, electrical or hydraulic, may be utilized to effect upward or closing motien of the lift rod 11 and conducting crossbar 10, or downward opening motion vof said lift rod 11 and attached conducting crossbar 10.

The contacts 8, 9 separate to establish an arc 12 (Fig. 3) within an orice 13, dened by an orifice sleeve member 14 enclosed in an insulating tube 15, the upper end of which is threadedly secured at 16 to a suitably configured support casting, generally designated by the reference numeral 17, and secured in any desired manner to the lower interior end of the terminal bushing 4.

, The gas disposed within the interior 18 of the exhaust tank 2 may be under any desired pressure, it merely being desirable to have this pressure, which may be above or below atmospheric pressure, at a value substantially half that of the gas disposed within a highpressure container, or reservoir, 20 disposed interiorly within the tank 2, adjacent the lower end thereof, as shown in Fig. 2 of the drawings.

By having SeF or SFB within the interior of the tank 2 advantage may be taken of the high dielectric strength of these gases Also because of the high dielectric esegesi Within av piston chamber 24. The. operation ofi the'blast.

valve 21 is brought` about by the actuation*l of a pilot'- valve assembly 25, which is: actuated, in turn, by a valve operating rod 2.6;,.secured. to and: movable with the. conducting. crossbar 10. from the high-pressure container'Zt) tothe blast valve 21which', it will be noted, isdisposedimmediately adjacent to the arc-extinguishing; unit 7, so that. therey will. be a minimum time delay, upon actuation of` the blast valve 21, for the gas to reach the orifice 13, and to quickly etlectA extinction of. theV established arc 12.

The. pilot-valve assembly 251 will now. be. described. A passage 28;;leads` from theuppen side of: the operating piston 23 of blast.v valve-21. to the'. pilot valve'. 30, which is secured to, and movablezwith, a valve stem 31; At the lower end of thevalve stem 31 is a roller 32, over which is latchedl a pivotally mounted latch 33, pivoted, as at 3.4 to theupper. end of the valve operating rod 26, as shown in. Fig. 2..of the drawings. Preferably a tension spring135. biases` the latch 33 about the rollerv 32; It will be. noted that at the. lowerf end of the latch; 33k is disposed a cam1portion136, which makes engagement with a relatively' stationary cam roller 37 for effecting release of the actuating rollerA 32l at an intermediate point` in' the opening operation.

From. the foregoing description, it will beapparentv that downwardi opening movement of v theconducting crossbar 150 and valvel operating rod 26 with the latch 33 pivotally supported on the latter, will" correspondingly effect downward' opening movement of the valve stem 31, and henceopening of the pilot valve'30. This will permit high-pressure gas, which is present withinthe blast tube 27 andi passage 38', to passabout the pilot valve 30, enterv passage 28 and actV upon the'upper side of operating piston123 This will effectY opening' of'tbe blast valve 21, against'the closing biasing action exertedV byy the diiferentialpressure onthis valve andv the compressionspring 22, toA permit the gas' to flow in the di# rection indicated by' the arrows 3'9v of Fig. 3 and to` exhaust through the oriiicemember 14 into the relatively lower pressure exhaust region within the interior 18 of; the exhaust tank 2;

It will be apparent' that the pressurewithin the highpressure reservoirV will be; lowered" to some extent by such an operation, andto maintain the pressure at a high-value within the high-pressure container 20, preferably at-a value substantially twice' that of thepressure withinthe exhaust region 18, a suitable-compressor 41 is. provided, which is electrically' connected' through a pressureV responsive. switch 42 to maintain the pressure withinthe high-pressure tank 20atV the desired value;

Asshown in Fig. 2', the compressor 4-1` forcesl highpressure gas through a one-wayvalve 43^ and through a: conduit 44 to be stored within the high-pressure-container- 20.

It will bey obvious 'fromv an inspection of Figs;- 2' and 3 that upon a predetermined downward' opening motion ofthe latch- 33, the cam` portion 3?6 thereofiwill" engage the stationary'roller 37 toeffect release of the actuating roller 32. At this point the spring- 45 will causere'- closure of the pilot valve 30. A leak 46 is provided byv a groove Within the upper end ofthe-valve stem 31- to: permit aslow" release'- of pressure' out of" the' region An: insulating, blast tube 27 leads.

4t 47 above the piston 23, to permit a gradual reclosure of the blast valve 21 following previous closure of the pilot valve 3i).

From the foregoing description it will be readily apparent as to the sequence of events which transpire during the opening operation. However, to recapitulate, in the closed-circuit position of the interrupter 1, the circuit extends'- therethroughby. wayjof terminal bushing 4,v contacts 8 and 9, through the conducting bridging member 1t?, and through the other extinguishingunitl'T (Fig. l) to the other terminaibushing' Duringfthe opening operation, which may be effected either automatically in response to overload.currents, ox:rnanually in accordance with the wishes o f` a. station attendant, suitable mechanism', which' may be' ofr` any conventional type, effects downward opening travel of the crossbar 1G, movable contacts 9 and both valve operating rods 26.

Wirth particular. reference: to Fig. 2,L the; downward movement of the latch33-will effect,4 opening ofxthe pilot, valve 36 to permit high-pressure gas tov pass: through` the passages 38, 2Stothe regionz47 aboveA the operating piston 23, This' will moveV the piston. 23v downwardlyY within the operating cylinder. 24 to effect. thereby. open.-` ing of the blast valve'21.. Tbiswill permit gas'athigh pressure Within the. highfpressure. reservoir 20A to pass upwardly through the blast-V tube: 27 and.' into. thel arcfextinguishing unit; 7,V in. a manner. indicatedA by the a1'. rows 39 of Fig. 3, to effect rapid extinction; of the.. two., arcs 12 associated with the. two serially. related. arc.- extinguishing, units 7'.. ,Y Y Y Shortly thereafter thecam. portionl 36 engages the. cam releaseroller 37 to etectzreleaseof thepilotzvalve.: stern 31 to permit the compression spring 45? toY efrect. reclosureofthe.. pilot. valve. assembly 25this preferably being, accomplished approximately attthetimethezmow able. contacts. 9reach their'l fullybpen position. Upon a. decreasein pressurewithinthe high-pressure reservoir. 20

the compressor 41, energized by operation of the. presY suretresponsive: switch 42:, will take; gas at. the` relatively low pressure present, withinA the exhaust'. region: 18,. and?` compress this gasl toia value suitablefor admissionlinto: ther high-pressures reservoir 20'. The. interrupter is now: in; theopen. positiont. y

To eiectareclosure .of theinterrupter, itislmerelyzneces sary for' the. operating: mechanism' to raise the lift; rod

11', causingV upward. closingmotion of.V the. crossbar" 10, and movable contacts. 9. At theend? of' theYV closingIV strokethe latches 332 willi he". forcedv laterally4 about the sides ofA the rollers: 32; tbisf action. beingv permitted by extension; of: the tension springs: 35. In tbe-completely` closed position of the-.interrupter 1', the latches 335. will` again. latch overthe rollers: 32 associated with` the lower end of the Vvalve stems-31 offthepilotvalvc assembliesZS.

Forcertainapplications it may' be desirable to provide a gas'4 ow through: the internupterI upon. reclosing. ofthe breaker. ln such an event, there is provided? auxiliary apparatus which mayabeattached to the other side oi'T theI top of the valve operating rod 26 to etect such a momentary. reopening-'of the pilot-valve assembly 25 during the closingaoperation.` As welll known; by those skilled inl the art, such. a blastfof gasduring. the closing` operation heipsfto prevent prestrikin'g of anfarc across=the approachingcontacts` 9, Y 8:. Y

The particular construction whichA I utilize comprises an upwardly projectingt arm 49, havinganactuating roller'- SO-'at the upper end thereof, as moreclearly shown inA Figs. 2, 3 and 4 of the drawings. Asnl operating` lever 52', pivotally mounted at astationarypivoty 53- to a downwardlyextending bracl,et-"portion54fv of the support casting=17; is biasedagainst a roller- 55l disposed at' tlievop positeside of-the lowerendl of the valvestenr 311 from the roll'erf 32', as` shownli'n Fig; 4'; A- Vtensi'on spring 56. maintains` theA operatingl lever 52 against; the upper` side of the roller 555- off' pilot-valve stem` 31. 'P l'nxsv upon upward closing motionl oi: the valve operatingj rod'l 2,

the roller S will forcibly effect clockwise rotation of the operating lever '2, as viewed in Fig. 2, to effect momentary opening of the pilot-valve assembly 25, in the manner previously described. Upon rotation of the operating lever 52, the roller S0 will slip by to permit the compression spring 45 to effect reclosure of the pilot valve 30. This will permit compression spring 22 to effect reclosure of the blast valve 21 in the manner previously described. Consequently a momentary blast of gas is obtained near the end of the closing operation.

It will be apparent that during the opening operation the operating lever S2 is rendered ineffective since it rotates in a counterclockwise direction about the pivot 53, as viewed in Fig. 2, having no effect upon the pilot-valve stem 31.

From the foregoing description it will be apparent that I have provided an improved compressed-gas type of circuit interrupter utilizing a tank essentially similar to the closed steel tank, provided with bushings, that is utilized in dead-tank oil breaker constructions. The contacts 9 may be operated by the conventional cross-arm mechanism. The exhaust tank 2 contains gas at relatively low pressure having the high pressure maintained within a suitable high-pressure reservoir associated with a portion of the tank structure. Although the high-pressure reservoir 20 is shown at the bottom of the tank 2, it could be placed in a different position, such as at the top of the tank 2. Although an orifice-type interrupter 7 has been illustrated, it will be obvious to those skilled in the art that other types of interrupters, such as crossblast interrupters, may be employed. y It will be noted that the leak 46 is rendered ineffective upon lowering of the pilot-valve stem 31 during the opening operation, and only becomes effective upon reclosure of the pilot valve 30. The compressor 41 may be located inside or outside of the breaker chamber, and senses a pressure drop within the high-pressure reservoir 20 as brought about by operation of the pressure responsive switch 42. In addition to the usual advantages of a dead-tank construction, such as a grounded case, bushing transformers, steel pressure enclosures, standard cross-arm mechanism, no external disconnect contacts etc., the construction described gives a high-pressure acoustic velocity flow without any discharge whatsoever to the outside of the tank. The blast valve is located very close to the interrupter, giving a minimum delay in starting the gas fiow. Another advantage is the unrestricted discharge into the large low pressure exhaust volume 18. This is of particular benefit in SFS interrupters because the large thermal expansion of the gas in the arc requires very free discharge passages to prevent stoppage of fiow during high-current interruption.

While a single interrupter is shown in Fig. 1, two or more interrupters in series per bushing can readily be used. In this case the series breaks are drawn simultaneously by lthe cross-arm movement, and gas for the units is supplied by a parallel connection to the inlet sides of the interrupters in an obvious manner. v Certain general aspects of the invention are set out and claimed in U. S. patent application, filed Decemberv 24, 1954, Serial No. 477,466, by Thomas E. Browne, Jr., and myself, and assigned to the assignee of the instant ap-` plication.

Although I have shown and described a specific structure, it is to be clearly understood that the same was merely for the purpose of illustration, and that changes and modifications may be readily made therein by those skilled in the art without departing from the spirit and scope of the invention.

I claim as my invention:

1. A circuit interrupter of the compressed gas type including a main tank. containing, gas, a pair ofv terminal bushings extending within the tank, a pair of arcextinguishing units disposed adjacent the interior ends of the terminal bushings, a conducting crossbar electrically. interconnecting the units, a pressure container con taining gas at a higher pressure than the main tank, a blast tube pneumatically interconnecting rthe pressure container with each arc extinguishing unit, and blast valve means actuated by opening movement of the crossbar for permitting high pressure gas to flow from the pressure container through the blast tubes and into the two arc-extinguishing units to effect extinction of the arcs drawn therein.

2. A circuit vinterrupter of the compressed gas type including a main tank containing gas, a pair of terminal bushings extending within the tank, a pair of arcextinguishing units disposed adjacent the interior ends of the terminal bushings, a conducting crossbar electrically interconnecting the units, a pressure container containing gas at a higher pressure than the main tank and disposed inside of the main tank, a blast tube pneumatically interconnecting the pressure container with each arc-extinguishing unit, and blast valve means actuated by opening movement of the crossbar for permitting high pressure gas to flow from the pressure container through the blast tubes and into the two arc-extinguishing units to effect extinction of the arcs drawn therein. 3. A circuit interrupter of the compressed gas type including a main tank containing gas selected from at least one of the group consisting of SFB and SeF, a pair of terminal bushings extending within the tank, a pair of arc-extinguishing units disposed adjacent the interior ends of the terminal bushings, a conducting crossbar electrically interconnecting the units, a pressure container containing the aforesaid gas at a higher pressure thanl the main tank, a blast tube pneumatically interconnecting the pressure container with each arc-extinguishing unit, and blast valve means actuated by opening movement of the crossbar for permitting high pressure gas to flow from the pressure container through the blast tubes and into the two arc-extinguishing units to effect extinction of the arcs drawn therein.

4. The circuit interrupter of claim 3, wherein the gas is admixed with at least one of the group consisting of nitrogen, air, argon, helium and carbon dioxide.

5. A circuit interrupter of the compressed gas type including a main tank containing gas selected from at least one of the group consisting of SP5 and SeFe, a pair of terminal bushings extending within the tank, a pair of arc-extinguishing units disposed adjacent the interior ends of the terminal bushings, a conducting crossbar electrically interconnecting the units, a pressure container containing the aforesaid gas at a higher pressure than the main tank and disposed inside of the main tank, a blast tube pneumatically interconnectting the pressure container with each arc-extinguishing unit, and blast valve means actuated by opening movement of the crossbar for permitting high pressure gas to ow from the pressure container through the blast tubes and into the two arc-extinguishing units to effect extinction of the arcs drawn therein.

6. The circuit interrupter of claim 5, wherein the gas is admixed with at least one of the group consisting of nitrogen, air, argon, helium and carbon dioxide.

7. A circuit interrupter of the compressed gas type including a main tank containing gas, a pair of terminal bushings extending within the tank, a pair of arcextinguishing units disposed adjacent the interior ends of the terminal bushings, a conducting crossbar electrically interconnecting the units, a pressure container containing gas at a higher pressure than the main tank, a compressor for taking gas from the main tank and compressing it for maintaining the gas supply in the pressure container, blast tube..means for pneumatically interconnecting the pressure: container with the two arcl extinguishing units, and blast valve means actuated by opening movement of the crossbar for permitting the flow of high pressure gas from the pressure container V' c throughA` theblast: tubemeanss'and into" the arceextinguishingunits. Y Y, i

Xi A circuit interrnpter of thecompressed; gas; type including a tank containing gas at a' relatively low'pres sure, aA pair of terminal bushings extending within theY tank, arpair of ,arcrextinguishing'units'disposed adjacent the interior end's of Ythe terminal bushings; a conducting crussbar electrically interconnecting 'the units; a' higlr pressure container containing gas at afrelativel'y 'high' pressure, a compressorI Vtortaking` gas at'th'e relatively l'ow'pressure' in the low pressure tank' and compressing itfor maintaining' the' gas supplyy inf-tbe high pressure container; blast tube means for pneumatically intercom-vV necting the' high pressure container` with the' two arcl extinguishingl units', blast valve means4 actuated: by' opening movement of'the crossbarfor permitting the iiow of high" Ypressure gas" from the` vhigh pressure container through'the blast'tub'e means andY into` the arc-extinguish-V ingv units, and' the blastvalve'v means being disposed immediately adjacent tul the arceextinguishing' units to eliminate any delay in starting' the blast of gas into'the units'.

9. A circuit interrupter' of the compressed' gas type including aA tank' containing gassa'tra relatively low'pres-v sure, a pair of terminal bushings extending within the tank, a4 pair of' arclextinguisliing units-'- disposed adjacent the interior' end/sV of theY terminalI bushings, a conducting crossbar electricallyI interconnecting the units; a high' pressure container containing gas at a relatively high pressure, a blast tube p'n'eumati'cally interconnecting' the high1 pressure container witha eaclr arc-extinguishing unit; a= blast valve associated with each unit, a pistonv fbr actuating' each blast valve; andlr a' two-way pilot valve for each unit actuated by opening movement ot the crossbar.

10. A- circuit interrupter of the compressed gas' Ytype including a tank' containing gas at a relatively low pres# sure, a pair of terminal bushings extending. within the tank, a pair of arc-extinguislling` unitsl disposed adjacent the interior ends of the terminal bushings, a conducting crossbar electrically'interconnecting the' units, a` high-pres- Y sureI container containing gas at' a relatively high pressure, a: blast tube pneumatically interconnectingv the'high pressure containerV with each`- arc-extinguishing unit, a blast valve: associated with each unit', af piston forv actuating each blast valve, a two-way pilot valve foreach unit'actu'- ated'- by'openi'ng' movement ofthe crossbar; andmeans for momentarily actuating the pilot'valve during the closing operationi to provide a blastA of gas at the unitsk during 'the closing operation.

' extinguishing units, a blast-'valve forl permitting high pres sure gas to flow` from saidl pressure' container into at least one unit and thence to exhaust into the main exhaust tank, said storage' tank containing gas at a relatively low pressure, and. pilot valvemeans lat'ched to the crossbarat least during a portion. oi the opening operation to'efect opening of the 'blastvalve j l2. TheV combination with a pair of arc-extinguishing units disposed in a V low pressuref exhaust taule of a conducting crossbar, a high pressure container,l conduit means interconnecting thehigh pressure container with the pair. of arc-extinguishing;units,.ablastvalve for permitting high pressure gas to flew from said'- high pressure container into ati least one unit and. thence into'said. exhaust tank, a piston for opening4 the blast' valve, anda twowayf pilot valve latche'd" to the. crossbar duringi atleast a part'ofithe opening operation.

1`3 The combination with` a4 pair of arcextingui'shing assegna-rf unitsclispo'sed'in"atlowpressure tank of a conducting cross.-V

' bar, azhighpressure container, conduit means interconopening tleblast'va'lve, a two-way'pilotvalve' latched'to the crossbarduringatlea'sta 4part ot the opening operation,andineans'connectedlto the crossbar for Voperating the 'twoV way pilot valve momentarily during theY closing operationtoobtain a closingbla'st'ofgas.

14, A compressed gascircfuitinterrupter including'a grounded metalli'c'rnaintank'iilled with gas Vand having a pair ofterrninalA bushings' extending therein, a pair of arc=extinguishing'units or' the gas-blast type secured to the interior ends of the terminal bushings, a lconducting crossbar electrically inter'cotrne'ctir'1g the two arc-extinf guishing units inserie'sirr the closedposition of thek interrupter,` a pressure container disposed within the; tank and containinggas" atlhigher pressure than; the. main tank, conduit means pneumaticallyinterconnecting the pressure container withthe two units, a blast valve associated with the conduitmeans, Aa piston` connected to the blast valve andV biased'toth'e'blast valve closed position, and means responsive'to movement of tliev 'crossba/r" for selectively applying high pressure or lbwerp'ies'sure gas to' thepiston to eiiectits operation. Y

15T' Av 'co'n'lp'ressedv gas' circuit interrupter including' a grounded metallic tank filled with low'pressure` gas and having at pair of"terrninalbushings extending therein, a pair ofl arc-extinguishing` units' of the gas-blast type se cured to the interior endsioftli'eterminal'bushingSLa con: ducting"crossbarelectrically intereonnectingv the' two arcextinguishing unitsin series inthe closed position ofV the interrupter, a" highl pressure container disposedv within the tank andcontaininggas at relatively highl pressure, conduit means pneumatically interconnecting the high pressurecontainer with the tworunits; av blastV valve associ'- ated' with theK conduit' means, al piston connected to the blastvalveand: biased to the'bl'ast valve closed positioma pilot valve'for applyingv low orhigh pressure to'said'piston, and' latching" meansf movable with the crossbar for n10- mentarily latching-ontthepilotivalve during the opening operation toieifectlits operation;

I6. A compressedJ gas circuit interrupter including' a grounded metallic tank lled wdithlow pressure lgas selected'from at'leastone-ofi the group consisting of SF antl- SeF'g'and having'apair' of 'terminal bushings'ext'ending' therein, a' pair of' arc-extinguishing units o'f` the gas-blast typesecured-to-the interior endsY of the terminal bushings, a conducting'crossbar' electrically interconnecting the two arc-extinguishing unitsin series in the closed position of the interrupter, ahigh pressure container disposed within the tank andlcontaining-the-aforesaid gas at relatively high pressure; conduitzmea-nspneumatically interconnecting the highy pressure containerwiththe two units, a blast valve associatedV with theV conduit means, a piston connected: to the blast valve and biasedto the blast valve closed position, and means responsiveto movementV of the crossbar for selectivelyapplying'highk pressure orlo'w pressuregas to the piston to eieetf itsy operation;

17A. The circuitfinterrupter of claim 16, wherein the gas is admixed withat least oneI of the group consisting Vof nitrogen, air, argon, helium and carbon dioxide.

ReferencesCtedin the leof' this patent UNTTED STATES PATENTS 2,108,560 Kesselring Feb. 15,1938 2,153,400 Trencham Apr. 4, 1939 2,221,720 PrnCe .NOM l2,A 1940 2,507,21Q Ludwig et. -'al;. .r... May Sii 195() Z;58l,57fl 'Baker' el: al.. ..-A... ..K............J.an.,. 8,. 19.5;2 

